The use of a hand operated pointing device for use with a computer and its display has become almost universal. By far the most popular of the various devices is the conventional (mechanical) mouse, used in conjunction with a cooperating mouse pad. Centrally located within the bottom surface of the mouse is a hole through which a portion of the underside of a rubber-surfaced steel ball extends. The mouse pad is typically a closed cell foam rubber pad covered with a suitable fabric. Low friction pads on the bottom surface slide easily over the fabric, but the rubber ball does not skid, but instead rolls as the mouse is moved. Interior to the mouse are rollers, or wheels, that contact the ball at its equator and convert its rotation into electrical signals representing orthogonal components of mouse motion. These electrical signals are coupled to the computer, where software responds to the signals to change by a .DELTA.x and a .DELTA.y the displayed position of a pointer (cursor) in accordance with movement of the mouse. The user moves the mouse as necessary to get the displayed pointer into a desired location or position. Once the pointer on the screen points at an object or location of interest, one of one or more buttons on the mouse is activated with the fingers of the hand holding the mouse. The activation serves as an instruction to take some action, the nature of which is defined by the software in the computer.
Unfortunately, the usual sort of mouse described above is subject to a number of shortcomings. Among these are deterioration of the mouse ball or damage to its surface, deterioration or damage to the surface of the mouse pad, and degradation of the ease of rotation for the contact rollers (say, (a) owing to the accumulation of dirt or of lint, or (b) because of wear, or (c) both (a) and (b)). All of these things can contribute to erratic or total failure of the mouse to perform as needed.
The underlying reason for all this trouble is that the conventional mouse is largely mechanical in its construction and operation, and relies to a significant degree on a fairly delicate compromise about how mechanical forces are developed and transferred.
Over the years, a number of optical techniques have been proposed for a computer mouse, but to date the mechanical mouse remains the most widely used pointing device. One recent optical development that appears likely to gain a significant degree of acceptance is that described in U.S. patent application Ser. No. 09/052,046, entitled SEEING EYE MOUSE FOR A COMPUTER SYSTEM, filed Mar. 30, 1998, by Gordon, Knee, Badyal and Hartlove and assigned to Hewlett-Packard Co. That Application discloses the use of techniques described in the aforementioned incorporated Patents to produce an optical mouse that navigates upon an arbitrary surface. The device disclosed therein is a non-mechanical mouse that is viable from a manufacturing perspective, relatively inexpensive, reliable, and appears to the user as essentially the operational equivalent of the conventional mouse. This new type of optical mouse has a familiar "feel" and is free of unexpected behaviors. It does not rely upon cooperation with a mouse pad, whether special or otherwise, but is instead able to navigate upon almost any arbitrary surface. It uses a single imaging integrated circuit to track translation of that circuit (and by implication, the mouse itself) across the arbitrary surface.
It is still a mouse, however, and needs some sort of surface to operate upon. Laptop computers and certain cluttered work environments are not hospitable to a mouse, whether conventional or optical. For example, the makers of laptop computers have gone to considerable trouble to provide mouse-like pointing sans the mouse. There have been joy sticks that pivot, stick-on track balls and pop-out pantographs, just to name a few. One laptop has a small stick that pops up between the keys and controls the screen pointer according to the force applied to it with a fingertip. Placed next to the "J" key on the keyboard, it has the advantage of letting the hands stay at the home position on the keyboard. Track balls and pantographs are either fussy or mechanically delicate, while the force sensing stick takes a lot of getting used to, as it does not translate one spatial position (hand/mouse combination) to another (screen pointer position). Instead, it moves the screen pointer in response to motionless pressure. There have been well designed and properly executed tests that show that screen pointer control paradigms that operate by translating a spatial position to become the pointer location (i.e., that involve actual movement) are faster and more accurate, and hence easier to use.
It would be desirable if the optical mechanism of the (above-mentioned) seeing eye mouse that allows tracking on an arbitrary surface could be adapted to allow position translation type screen pointer control, but without an actual mouse or other moveable appendage that wears, binds or gets bent or broken off entirely. It would be a further advantage if such an optical mechanism also allowed the hands to remain at the home position on the keyboard. What to do?